Add new type to abstract away client id or client instance

Inspired by ruby on rails active record where you can also
pass full instances or only integer ids and the framework
will figure it out.

Author: ChillerDragon

library/ddnetpp.lua

@@ -214,12 +214,14 @@ ddnetpp = {
 	},
 }
 
+---@alias ClientId integer|Character|Player
+
 ---Sends a server chat message to everyone.
 ---@param message string # The message to be displayed in chat
 function ddnetpp.send_chat(message) end
 
 ---Sends a server chat message to one specific client.
----@param client_id integer # The recipient of the message
+---@param client_id ClientId # The recipient of the message
 ---@param message string # The message to be displayed in chat
 function ddnetpp.send_chat_target(client_id, message) end